1. Field of the Invention
The present invention relates to a display apparatus and, more particularly, to an image signal processing apparatus and method which are suitable for a large display panel such as a liquid crystal projector.
2. Related Background Art
Conventionally, for non-interlaced display of a TV image signal as an interlaced image signal on a liquid crystal display device, the following attempts (1) and (2) have been made as disclosed in Japanese Patent No. 2727583 in which vertical resolution is increased, and flicker in image is reduced using a line memory, field memory, or frame memory.
(1) Assume that a TV image is displayed on, e.g., a liquid crystal display. A TV image signal is an interlaced signal that forms one image by two fields (=one frame). In Japan, the frame frequency is 30 Hz, and the update period of an image signal of one scanning line is 30 Hz. When a TV image is displayed on the liquid crystal display in the interlace mode, the rewrite frequency of image data of one scanning line is 30 Hz. This appears as flicker on the screen because of the holding characteristics of the liquid crystal, resulting in very poor image quality.
(2) To prevent this flicker, an image is formed using, e.g., a line memory in a pseudo non-interlace mode.
FIG. 8 shows a display section for such image display. In the odd-numbered field, one image signal is displayed on the first line, image signals of the same scanning line are displayed on the second and third lines, . . . , image signals of the same scanning line are displayed on the (2n)th and (2n+1)th lines. In the even-numbered field, image signals of the same scanning line are displayed on the first and second lines, . . . , image signals of the same scanning line are displayed on the (2nxe2x88x921)th and (2n)th lines. The image data rewrite frequency is 60 Hz that is equal to the field frequency. Hence, no flicker occurs, and vertical resolution does not degrade.
In the conventional liquid crystal projector, a conventional line doubler is used for de-interlace by the method (1) or (2). However, in the method (2), the image quality is degraded by line flicker, and characters are difficult to recognize because of low resolution. In the method (1), images of consecutive odd- and even-numbered fields are simultaneously displayed on one frame, a movie is displayed as a double image. A method of discriminating between a still region and a movie region in one frame and processing them by different processes has also been developed. However, high cost due to an increase in frame memory or hardware poses a problem.
Under these circumstances, a demand has arisen for an apparatus and method capable of realizing optimum display for each of a still image and a movie at low cost.
Especially, in a liquid crystal projector which projects an image for magnification display, relative degradation in resolution due to magnification display or line flicker in the interlace mode (a display image flickers at its edge portion in units of lines because scanning lines of odd-numbered lines and scanning lines of even-numbered lines are alternately displayed in interlaced display) is conspicuous and poses a serious problem for a large display panel.
The present invention has been made in consideration of the problems of the prior art, and has as its object to enable, at low cost, image display with little line flicker based on an interlaced image signal and satisfactory movie display characteristics.
In order to achieve the above object, according to the present invention, the first de-interlace mode in which interlaced scanning line signals in the consecutive odd- and even-numbered fields are received by storage means, and the scanning line signals in the consecutive odd- and even-numbered fields are alternately read out to perform de-interlacing, and the second de-interlace mode in which scanning line signals in the odd- or even-numbered field are read out in units of fields and magnified in the vertical direction to perform de-interlacing are prepared. The scanning line signals are compared between the fields to determine whether the signal is a movie or a still image. When it is determined that the signal is a still image, the signal is displayed on a display device using a non-interlaced signal obtained in the first de-interlace mode. When it is determined that the signal is a movie, the signal is displayed on the display device using a non-interlaced signal obtained in the second de-interlace mode.
De-interlace used in this application will be described below.
In the current TV broadcasting, one image (one frame) is segmented into two images, i.e., an image of odd-numbered lines and an image of even-numbered lines (these images are called an odd-numbered field and even-numbered field, respectively), and transmitted. In a TV (CRT), the odd-numbered field image is displayed on odd-numbered lines of the CRT, and the even-numbered field image is displayed on even-numbered lines of the CRT. This display scheme is called interlaced display.
In a display (CRT or LCD) used for a personal computer or the like, image data of one frame is sequentially displayed on odd- and even-numbered lines without segmenting the image data into odd- and even-numbered fields. This display scheme is called progressive display.
To display a current TV broadcasting signal on the display of a personal computer or the like in the progressive display mode, the interlaced signal must be converted into a progressive signal. This conversion is called de-interlace. In Japan, it is also called non-interlaced display.